the hosts could try a trial based membership, e.g. if the member hasn't contributed to the forum in a positive manner they could be banned for a time or their account deleted. This way if the member’s account can be deleted if they don’t post sufficient helpful & meaningful (not spam) post or if all the member does is rubbish very one else then they too can be deleted or suppended from thr forum for a time.

Just some ideas. :D